A glass that has been whitened by incorporating particles having different refractive indices and the like into transparent glass so as to cause light scattering therein, or by uniformly dispersing a certain amount of opaque fine particles from the beginning, and thereby reducing light transmittance, is generally called milky white glass, opaline glass, or white glass. Due to its satisfactory aesthetic appearance and storage stability, whitened glass is used in containers, tableware, construction materials and the like.
Here, conventional white glass compositions usually contain predetermined amounts of fluorine, and milky whitening is achieved by uniformly dispersing a crystalline phase of NaF as a milky white component in a glass phase of SiO2 as a main component (see, for example, Patent Document 1).
More specifically, disclosed is a white glass composition including 70% to 73% by weight of SiO2 and 4% to 6% by weight of fluorine, and white glass containers are formed using that composition.
On the other hand, a method for producing crystallized glass formed from a glass composition that does not include fluorine has been proposed (see, for example, Patent Document 2).
More specifically, disclosed is a method for producing an opaque (white) crystallized glass containing phosphorus, the method being characterized in that glass is molded using a glass composition which includes a predetermined glass composition including 45% to 65% of SiO2, 3% to 15% of Al2O3, 10% to 25% of Na2O, 12% to 25% of CaO, and 3% to 8% of P2O5, all on the basis of percentage by weight, at a proportion of 90% by weight or more of the total amount, and the molded glass is gradually cooled, subsequently subjected to a post-heat treatment at about 900° C., and crystallized.
Furthermore, the applicant of the present invention has proposed a milky white glass composition that does not contain a significant amount of fluorine, can be produced safely and easily, exhibits superior white coloration, and can be melted at low temperature (see, for example, Patent Document 3).
More specifically, disclosed is a milky white glass composition including 35% to 65% by weight of SiO2, 3.5% to 10% by weight of P2O5, 5.5% to 15% by weight of Al2O3, and 3% to 15% by weight of CaO, which gives milky white glass only by melting a predetermined glass raw material at about 1400° C. and then slowly cooling the material.